[P5.3] Define Topic Map Specification v1 (vendor-neutral, citable)

[MTCMarkFranco]

Goal

A versioned specification document for the Topic Map format. Vendor-neutral. Citable. Other implementations can claim conformance.

Why this matters

This is what turns lambda-rag from "an implementation" into "the reference implementation of an open spec." Critical for pattern adoption beyond your repo. Other tools should be able to consume topic maps without reading lambda-rag's source.

Acceptance criteria

• spec/topic-map-v1.md written: schema, semantics, conformance requirements, examples.
• JSON Schema / formal grammar provided.
• Conformance test suite (separate repo or spec/conformance-tests/).
• Spec versioned independently of lambda-rag.
• Spec announcement post — invite ecosystem.